In this article we look at the impact of psi-values and why they matter. Psi-values are a measure of the heat loss of a junction between two fabric elements, eg floor and external wall. These junctions are called non-repeating thermal bridges.
Previous iterations of the UK Building Regulations have raised awareness of the importance of fabric u-values and air tightness, the incoming revision is set to sharpen the focus on the ‘non-repeating’ or ‘linear’ thermal bridges that occur at junctions between fabric elements. The easy option of using Accredited Construction Details (ACD) will disappear from SAP as a new version is introduced next summer. This will force developers to more strongly consider junctions when choosing their building fabric or to have the heat loss properties of their junctions evaluated by trained specialists in order to avoid having to assume worst-case default heat losses.